In this photo released by CBS, “NCIS” star Mark Harmon, left, laughs while host David Letterman holds up an old photo of him as a college football player, on the set of “The Late Show with David... more 
In this photo released by CBS, “NCIS” star Mark Harmon, left, laughs while host David Letterman holds up an old photo of him as a college football player, on the set of “The Late Show with David Letterman,” Wednesday, May 10, 2011, in New York. less 
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Associated Press | Photo By CBS, Heather Wines
Tue, May 10, 2011 7:05 PM EDT